The newborn Earth “ate” several embryos of the planets after its collision with Teia, the progenitor of the Moon, traces of which geologists found in the oldest rocks of the planet in Greenland.
“We built computer models of how the newborn Earth collided with other celestial bodies, and how their metals and silicates mixed with the matter of our planet at a time that we call” the era of late accretion. “These calculations show that the earth’s bowels contain much more similar matter than our colleagues thought, which greatly changes the history of its evolution, “Simone Marchi, of the Southwest Research Institute in Bower, USA, said.
The Mysteries of the Moon
For the last 30 years it has been assumed that the Moon was formed as a result of the collision of Teiya, a protoplanetary body, with the “embryo” of the Earth. The collision led to the ejection of the matter of Teiya and proto-Earth into space, from this matter the Moon was formed. The theory of collision of proto-Earth with a large celestial body explains well the mass of the moon, the small iron content on it and other parameters.
However, in such a collision, a significant part of the material constituting the moon was to be brought by the hypothetical Teia. In its composition it had to differ from the Earth, as differs from it most of the celestial bodies of the inner region of the solar system, which includes the terrestrial planets and asteroids. But in fact the composition of the Earth and the Moon is very similar, up to the same proportion of isotopes of many metals and other elements.
Despite all the advantages of this hypothesis, she has several serious shortcomings. For example, in accordance with this idea, all the water reserves had to completely evaporate from the matter of the future Moon at the moment when it was thrown into space after the clash between Teiya and Earth.
Six years ago, many astronomers began to doubt this, because the water shares in some samples of rocks brought to Earth by the Apollo 15 and Apollo 17 expeditions were hundreds of times higher than the theoretically predicted values. Other scientists suggested that NASA astronauts came across a kind of “water anomaly”, analogues of which on the Moon may not be.
Markhi and his colleagues suggest that almost all of these anomalies could have been generated by the fact that the Earth collided not only with Teia, but also with a host of other germs of planets, a significant part of whose matter is now hidden in the bowels of our planet.
Traces of a space meal
They came to this conclusion by creating a computer model of a newborn solar system that was inhabited not only by the Earth and the Moon, but also by a multitude of planetsimals, the “dead” embryos of planets that periodically collided with our planet and other celestial bodies.
As scientists believe today, the Earth had to survive dozens or even hundreds of such clashes. Most of the matter of such embryos of the planets had to evaporate into space or be thrown out there during the collision with the Earth, as a result of which only 0.5% of its mass today falls on the matter of “alien” worlds.
The calculations of the Marha team showed that this is not so. If at least a small part of these planetsimals were large enough, more than 1500 kilometers across, then the earth’s interior consists of approximately 2.5-3% of the rocks formed in the bowels of other planets.
How to find traces of these planets? According to geologists, the force of these collisions was not high enough for the crust and mantle of the Earth to completely melt and mix with the “alien” rocks, but it was enough for the fragments of the former embryo of the planet to penetrate to great depth.
This means that in the bowels of the planet there must be areas with anomalous isotopes of different metals, such as tungsten and hafnium, as well as unusual silicate rocks, analogues of which no longer exist anywhere on our planet. According to Markhi and his colleagues, their deposits are found in Greenland, in the so-called greenstone belt.
Here, according to them, they often find unique breeds of komatites containing anomalously high fractions of tungsten-182 and having an unusual structure that are not found anywhere else on Earth. Their study, according to Markhi, will help us understand how many other planets the Earth ate and how it looked in the first moments of its life.